But even if we start out with a child-like image of God as the great vending machine in the sky, nevertheless the act of turning to God to ask Him for our desires is already itself an implicit acknowledgement that He is creator and Lord of all. Sincere prayer, even if imperfect in object, helps us adjust our attitudes, our perceptions - it humbles us.
One may wonder, if God knows our every need, why is it we need to pray anyway? The answer is, because prayer isn't to help God, it's to help us. Petitioning God first and foremost causes us to recognize our relationship with God as dependent upon Him, and therefore requires humility to even begin to ask for anything.
The catechism explains:
2629 The vocabulary of supplication in the New Testament is rich in shades of meaning: ask, beseech, plead, invoke, entreat, cry out, even "struggle in prayer." Its most usual form, because the most spontaneous, is petition: by prayer of petition we express awareness of our relationship with God. We are creatures who are not our own beginning, not the masters of adversity, not our own last end. We are sinners who as Christians know that we have turned away from our Father. Our petition is already a turning back to him.
Secondly, it requires us to think about what it is we need and why, and therefore helps us to prioritize and hopefully, with maturity and humility, to stop pestering God for that million dollars to drop from the sky and realize that what we should really be asking for (in other words, what we really need) is more patience/humility/charity/[insert virtue here], and not necessarily more stuff.
Of course, one of the primary things we should be asking for often is God's forgiveness. Once again, this requires humility, it also requires repentance, an acknowledgement of wrongdoing and a willingness to accept the grace needed to stop.
2631 The first movement of the prayer of petition is asking forgiveness, like the tax collector in the parable: "God, be merciful to me a sinner!" It is a prerequisite for righteous and pure prayer. A trusting humility brings us back into the light of communion between the Father and his Son Jesus Christ and with one another, so that "we receive from him whatever we ask." Asking forgiveness is the prerequisite for both the Eucharistic liturgy and personal prayer.
Our God is merciful and loving, ready and willing to forgive us our sins when we acknowledge them and turn from them, desiring to give us our every need. The catechism says that "Christ, who assumed all things in order to redeem all things, is glorified by what we ask the Father in his name." And so let us ask boldly and with confidence, glorifying God in acknowledging His sovereignty.
But if any of you lacks wisdom, he should ask God who gives to all generously and ungrudgingly, and he will be given it. (James 1:5)
Ask and it will be given to you; seek and you will find; knock and the door will be opened to you. For everyone who asks, receives; and the one who seeks, finds; and to the one who knocks, the door will be opened.
Which one of you would hand his son a stone when he asks for a loaf of bread, or a snake when he asks for a fish? If you then, who are wicked, know how to give good gifts to your children, how much more will your heavenly Father give good things to those who ask him. (Matt 7:7-11)